Carrying capacity is typically defined as the maximum that can be supported indefinitely by a given environment. The simplicity of this definition belies the complexity of the concept and its application. There are at least four closely related uses of the term in basic , and at least half a dozen additional definitions in .

Basic Ecology Carrying capacity is most often presented in ecology textbooks as the constant K in the logistic population growth equation, derived and named by Pierre Verhulst in 1838, and rediscovered and published independently by Raymond Pearl and Lowell Reed in 1920:

where N is the population size or density, r is the intrinsic rate of natural increase (i.e., the maximum per capita growth rate in the absence of ), t is time, and a is a constant of integration defining the position of the curve relative to the origin. The expression in brackets in the differential form is the density-dependent unused growth potential, which approaches 1 at low values of N, where logistic growth approaches exponential growth, and equals 0 when N=K, where population growth ceases. That is, the unused growth potential lowers the effective value of r (i.e., the per capita birth rate minus the per capita death rate) until the per capita growth rate equals zero (i.e., births=deaths) at K. The result is a sigmoid population growth curve (Figure 1). Despite its use in ecological models, including basic fisheries and wildlife yield models, the logistic equation is highly simplistic and much more of heuristic than practical value; very few populations undergo logistic growth. Nonetheless, ecological models often include K to impose an upper limit on the size of hypothetical populations, thereby enhancing mathematical stability.

[Of historical interest is that neither Verhulst nor Pearl and Reed used ‘carrying capacity’ to describe what they called the maximum population, upper limit, or asymptote of the logistic curve. In reality, the term ‘carrying capacity’ first appeared in range management literature of the late 1890s, quite independent of the development of . Carrying capacity was not explicitly associated with K of the logistic model until Eugene Odum published his classic textbook Fundamentals of Ecology in 1953.] The second use in basic ecology is broader than the logistic model and simply defines carrying capacity as the equilibrial population size or density where the birth rate equals the death rate due to directly density dependent processes. The third and even more general definition is that of a time. In this case, the birth and death rates are not always equal, and there may be both immigration and emigration (unlike the logistic equation), yet despite population fluctuations, the long-term population trajectory through time has a slope of zero. The fourth use is to define carrying capacity in terms of Justus Liebig’s 1855 law of the minimum that population size is constrained by whatever is in the shortest supply. This concept is particularly difficult to apply to natural populations due to its simplifying assumptions of independent limiting factors and population size being directly proportional to whatever factor is most limiting. Moreover, unlike the other three definitions, the law of the minimum does not necessarily imply population regulation. Note that none of these definitions from basic ecology explicitly acknowledges the fact that the population size of any species is affected by interactions with other species, including predators, parasites, diseases, competitors, mutualists, etc. Given that the biotic environment afforded by all other species in the typically varies, as does the abiotic environment, the notion of carrying capacity as a fixed population size or density is highly unrealistic. Additionally, these definitions of carrying capacity ignore evolutionary change in species that may also affect population size within any particular environment.

B

A

Fig: Logistic growth curve and carrying capacity: A: From Peter Stiling; B: From Ricklefs & Miller Applied Ecology: The term carrying capacity may have first appeared in an 1898 publication by H. L. Bentley of the United States Department of Agriculture, with an original focus on. maximizing production of domestic cattle on rangelands of the US southwest. The first use in wildlife management was apparently associated with classic studies of deer populations on the Kaibab Plateau in northern Arizona in the 1920s. The concept was popularized in wildlife ecology by Aldo Leopold and Paul Errington in the 1930s. There have been four typical uses of carrying capacity in applied ecology, illustrated in Figure 2: (1) the maximal steady-state number or of animals an area can support in the absence of exploitation (the original use of carrying capacity, K); (2) the maximal sustainable yield (MSY) of biomass of animals an area can produce for exploitation, which equals 0.5K in the simplest form of the logistic model; (3) the maximal sustainable economic yield (MEY) of animals an area can produce for exploitation, which equals the maximum difference between yield value and cost of exploitation; and (4) the open-access equilibrium (OAE), where the value of the yield equals the cost of exploitation, which is the upper economic limit of exploitation in the absence of economic subsidies and restrictive management regulations. Note that open access, typical of historical marine fisheries, often leads to severe because the population is reduced to sizes far below the other types of carrying capacity. Indeed, even the application of maximum sustainable yield in single species has proven elusive and often disastrous, as evidenced by the poor state of most marine fishery stocks so managed. Two

additional uses of carrying capacity in applied ecology focus on optimal stocking of rangeland with cattle, sheep, etc. The Society for Range Management defines the term as the maximum stocking rate possible which is consistent with maintaining or improving vegetation or related resources. A more general definition is the optimum stocking level to achieve specific objectives given specified management options. These practical definitions implicitly acknowledge that carrying capacity is not a constant, but rather is affected by a variety of environmental factors.

ECONOMIC CARRYING CAPACITY Economic carrying capacity is defined by management goals for population , animal quality and conditions but is determined by a habitat’s variable and limited ability to sustain achievement of these goals. Economic carrying capacities defined by management goals for population productivity and for population control are termed maximum harvest density and minimum impact density. Maximum harvest density The concept is usually applicable to ungulates. It is the number of animals that a habitat will support while producing a maximum sustained harvestable surplus. In terms of the sigmoid model, the population is at or somewhat above the inflection point. The population must be maintained at this level of by harvest. Therefore no lack of welfare factors prohibit the growth of a population Impact on wildlife populations & its habitat 1. At maximum harvest density, population quality will be very good though not probably the very best possible. 2. Populations at MHD characteristically exhibit a young age structure and high rate of turnover 3. Habitat condition will also be good though not without signs of use and perhaps retrogressed vegetation Minimum impact density Minimum impact density as a goal for wildlife management aims to reduce the impact of wild animals on those of desirable target species. It may be desirable to maintain a population at MID of carrying capacity if - The population is considered to be a pest species, one not to be eliminated but to be controlled - The predator population depresses the production of livestock or desirable wildlife species

- Ungulates compete with valuable and perhaps less competitive wildlife species target of a particular management programme Impact on wildlife population and its habitat 1. Populations maintained at Minimum impact density of carrying capacity have a very low level of ecological density. 2. Reproduction and resistance to natural mortality is generally high in such populations, requiring persistent and abundant harvest of animals to maintain the population at this level. 3. The population habitat should also be in excellent condition, receiving only minor use from the depressed population. “Ecological carrying capacity is a variable habitat characteristic determined by changeful amounts of welfare factors that limit the size and productivity of a species population.” Sometimes populations are unharvested, or normal levels of harvest do not influence the population size very much. In these cases carrying capacities are determined only by limiting habitat resources, and it is often useful to distinguish which set of limiting resources is important in determining population size. Ecological carrying capacity as determined by limiting amount of forage or interspersion and of space is termed as subsistence density, security density and tolerance density respectively. Subsistence density It is the size of an unharvested population limited primarily by forage. In terms of the sigmoid model subsistence density occurs at the upper asymptote. Impact on wildlife population and its habitat 1. At subsistence density, population quality and habitat condition will be comparatively poor because this is the ultimate in ecological density. 2. Reproduction is expected to be low and periodic die-off’s will probably occur in years of severe weather. 3. Subsistence density implies that the primary limitation on reproduction and survival is food Tolerance Density Tolerance density is the number of animals that a habitat will support when intrinsic behavioral and/or physiological mechanisms are dominant in controlling the population. It is sometimes also called as saturation point density and is especially characteristic of territorial species. In terms of sigmoid model, tolerance density occurs at the upper asymptote. For populations at tolerance density, both spaces as well as intraspecific competition become limiting welfare factors. Impact on wildlife population and its habitat 1. At tolerance density, all animals may be in good condition or they may be in a hierarchy of condition. 2. The subordinate animals will be in the poorest of condition having low rates of reproduction and survival. 3. Since animals tend to defend resources, there is little or no degradation of limiting factors and therefore the habitat condition is also good. Security density Security density as a concept of carrying capacity is the number of animals a habitat will support when welfare factors necessary to alleviate are limiting. These welfare factors are escape cover, interspersion and for some animals space. In the sigmoid model security density is at the upper asymptote. Impact on wildlife population and its habitat 1. At security density, social intolerance may force some animals out of the secure habitat. These animals then suffer high predation losses. 2. Reproduction by dominant animals is high and these animals are in good condition too. 3. Habitat condition should also be good.

Fig. 3

History of carrying capacity: Carrying capacity was first applied to biological systems in the 1870s, however, it retained its literal application; in this use, it referred to the mass of meat that pack animals could physically transport (Fig. 3a). Sayre (2008) attributes the evolution of carrying capacity from a literal and quantitative concept to a figurative and qualitative concept from its application to livestock populations “being carried by the land where they lived” in the 1880s. From this moment on, carrying capacity referred to a quasi- quantitative amount of something that could be “carried by the environment.” The contemporary usage of carrying capacity was further shaped in the 1950s from the logistic curve originally developed over 100 years prior. In fact, it was not until the first edition of Fundamentals of Ecology when Odum (1953) assigned the term “carrying capacity” to the asymptote of the logistic curve, though there was very little empirical evidence of such a thing. Before, according to Sayre (2008), the asymptote of the logistic curve was “simply an upper limit of growth.” This new development undoubtedly influenced a generation of biologists, particularly at the population level of ecology though there is considerable interest at several levels of ecological organization and continues to be widely applied in the literature. This conceptual evolution of carrying capacity developed independently from the human carrying capacity approach (see Vogt, 1948) that is commonly used in the sustainability and development literature, despite sharing a common conceptual ancestor (Fig. 3a). In this study we focus on the former application of carrying capacity the application more commonly associated with understanding biotic interactions in that is independent of social implications in the context of intrinsic limits of populations in ecosystem studies. carrying capacity is most often used and applied: aquaculture, rangeland management, wildlife management, conservation biology, and fisheries biology (Fig. 3b).

Carrying capacity and Wildlife Biology: The term carrying capacity is one of the most common phrases in wildlife management. It does, however, cover a variety of meanings and unless we are careful and define the term, we may merely cause confusion. Some of the more common uses of the term are discussed below. Concepts such as population size, “carrying capacity,” and have long been central in the fields of wildlife management and conservation biology. Because conservation biology is often concerned with single species at risk for extinction and focus on the population level, it is intuitive that these studies use carrying capacity to investigate species viability. Given that conservation biologists and wildlife managers are historically most often interested in populations and dynamics of populations, including concepts such as birth rates, death rates, and K the intrinsic limit of a population the application of carrying capacity in wildlife management and conservation biology is a natural extension and application of the concept.

In the management of wildlife there is a diverse range of factors that need to be considered when determining ecological carrying capacity. These include::  Habitat preference  Food preference  Territoriality  Interspecies competition  Habitat protection The issue is also further complicated by the management objectives of the reserve manager and ecologist. Game reserves may be managed for game viewing, trophy hunting, venison production or game farming. Thus, various options in terms of the ecological carrying capacity are available. These include:  Economic carrying capacity  Maximum harvest density  Minimum impact density  Maintenance density  Tolerance density Prey–Predator Models with Variable Carrying Capacity: Prey–predator dynamic is an essential tool in mathematical ecology, specifically for our understanding of interacting populations in the . The effect of variable carrying capacity in prey- predator relationship; that is, the periodicity in the solutions of the system decreases in magnitude and reaches the stable equilibrium faster than the system with constant carrying capacity. Finally, when the death rate of predators, which was taken to be the bifurcation parameter, was increased, the prey and the predator dynamics changed from having periodic behaviour that, by exhibiting damped oscillations and reaching an asymptotically stable spiral equilibrium point representing the co-existence of both populations, reached a stable limit cycle for small values of the death rate of the predator to a situation where the two populations reach an asymptotically stable point representing the existence of the prey population only in the case of the higher predator’s death rate. Prey–predator models with variable carrying capacity are corelated with following aspects. [1]. All populations are affected by changes in their environment; therefore, there is a need to treat the carrying capacity as a system variable (i.e., function of time) in order to model population dynamics in an environment that undergoes changes [2]. In particular, in resource management, where the carrying capacity is often assumed to be constant and unchanging [3]. Many efforts to predict the world’s carrying capacity, the maximum sustainable population, are based on this assumption [4]. However, technological developments have raised crop yields, allowing a greater population to be supported by a smaller land area [5]. Thus, for the human population, a constant carrying capacity is not realistic [6]. Similarly, in nature, the inherent variability of natural systems [7] means that assuming an unchanging carrying capacity fails to adequately represent the environment.

[A classic field study of wildlife carrying capacity was published by David Klein in 1968. In 1944, some two dozen reindeer were released on St. Matthew Island in the Bering Sea, where previously there had been none. Lichens were plentiful and the population increased at an average rate of 32% per year for the next 19 years, reaching a peak of about 6000 in 1963. During the severe winter of 1963–64, nearly all the animals died, leaving a wretched herd of 41 females and 1 male, all probably sterile. It was not so much the inclement weather that devastated the herd as it was a deficiency in food resources caused by overgrazing. After careful study, Klein concluded that 5 reindeer per square kilometer would have been the carrying capacity of an unspoiled St. Matthew Island. An animal census taken in 1957 gave 4 animals per square kilometer. A further 32% increase during the ensuing year brought the population to 5.3 per square kilometer, in excess of the predicted carrying capacity and a prelude to the eventual population crash.]

What will be happens if carrying capacity exceed? A list of studies that address implications of exceeding ecosystem carrying capacity or implications of “overshooting” the ecosystem carrying capacity. The most common ecosystem-level implications of overshooting carrying capacity in the studies were: 1) a decrease in species and richness; 2) a decrease in primary productivity; 3) changes in biogeochemical cycling ; 4) an increase in the vulnerability to invasions (increase in non-native invasion) and 5)Ecosystem state change, / interactions, ecosystem collapse, ecosystem destability. In addition to these 5 commonly discussed implications of overshooting carrying capacity, several studies discussed decreases in carbon sequestration. As a whole, the evaluated studies suggest that the magnitude of the ecosystem level response depends on the magnitude of carrying capacity overshoot (Fig. 4). For example, at a relatively small magnitude of carrying capacity overshoot, a small magnitude ecosystem response a small decrease in primary productivity or a small decrease in biodiversity would be expected. However, if the magnitude of

carrying capacity overshoot is large enough, a threshold may be crossed and the ecosystem may change states (Fig. 4). Once in the alternate state, a small magnitude carrying capacity overshoot in the new state may lead to new additional changes in biodiversity, ecosystem productivity, or elemental cycling, whereas a large magnitude carrying capacity overshoot may lead to more impactful changes related to ecosystem stability or state changes

Fig. 4:

Shootable surplus: The number of individuals of a population which are in excess to the carrying capacity of the habitat is called shootable surplus. Carrying capacity and : The carrying capacity of a biological species in an environment is the maximum population size of the species that the environment can sustain indefinitely, given the food, habitat, water, and other necessities available in the environment. In population biology, carrying capacity is defined as the environment's maximal load, which is different from the concept of population equilibrium. Its effect on population dynamics may be approximated in a logistic model, although this simplification ignores the possibility of overshoot which real systems may exhibit. Carrying capacity was originally used to determine the number of animals that could graze on a segment of land without destroying it. Later, the idea was expanded to more complex populations, like humans. For the human population, more complex variables such as sanitation and medical care are sometimes considered as part of the necessary establishment. As population density increases, birth rate often increases and death rate typically decreases. The difference between the birth rate and the death rate is the "natural increase". Is the carrying capacity could support a positive natural increase or could require a negative natural increase. Thus, the carrying capacity is the number of individuals an environment can support without significant negative impacts to the given organism and its environment. Below carrying capacity, populations typically increase, while above, they typically decrease. A factor that keeps population size at equilibrium is known as a regulating factor. Population size decreases above carrying capacity due to a range of factors depending on the species concerned, but can include insufficient space, food supply, or sunlight. The carrying capacity of an environment may vary for different species and may change over time due to a variety of factors including: food availability, water supply, environmental conditions and living space. Ecological footprint

One way to estimate human demand compared to ecosystem's carrying capacity is "ecological footprint" accounting. Rather than speculating about future possibilities and limitations imposed by carrying capacity constraints, Ecological Footprint accounting provides empirical, non speculative assessments of the past. It compares historic regeneration rates, biocapacity, against historical human demand, ecological footprint, in the same year. Most recent results from Global Footprint Network's data platform show that humanity's footprint exceeded the planet's biological capacity in 2016 by over 70% (a 2002 publication reported overshoot for 1999 at>20%). However, this measurement does not take into account the depletion of the actual fossil fuels, "which would result in a carbon Footprint many hundreds of times higher than the current calculation. "There is also concern of the ability of countries around the globe to decrease and maintain their ecological footprints. Holden and Linnerud, scholars working to provide a better framework that adequately judge sustainability development and maintenance in policy making, have generated a diagram that measures the global position of different countries around the world, which shows a linear relation between GDP PPP and ecological footprint in 2007. According to the Figure 5 diagram, the United States had the largest ecological footprint per capita along with Norway, Sweden, and Austria, in comparison to Cuba, Bangladesh, and Korea.

Fig. 5

[For countries in category A, as are most developing countries, the main objective of a sustainable development strategy would be to improve their economies. Most likely, as indicated by the regression line, this would imply an increase of their per capita ecological footprint. Countries in category B should promote policy measures that ensure that they hold their position within the SDA and concentrate on fulfilling the prima characteristics of sustainable development. The imperative for countries in category C is to reduce their ecological footprint. Third, for countries in category C, which includes all OECD countries, sustainable development primarily means reducing their average per capita ecological footprint. True, there are large variations in the footprints of developed countries. Getting into the SDA would require substantial effort by the USA, Finland, Sweden and Norway, whereas less effort would be required by Japan, Italy, Austria and the Netherlands]

Source: Peter Stiling

Estimation of carrying capacity:

Source: S.K. Singh

Source: Peter Stiling: Ecology

Application: The application of carrying capacity in ecosystem studies showed that: 1) because of its strong historical ties to population dynamics, carrying capacity is most often applied at the population level commonly defined as the number of individuals per unit are- though there were over a dozen explicit definitions across all levels of ecological organization; 2) carrying capacity is often considered dynamic with relation to both time and space; 3) carrying capacity is distally controlled by energy availability and proximally by habitat and food availability; 4) when required resources exceed available resources there are negative impacts on ecosystems including, a decrease in productivity, biodiversity, and richness, and an increase in vulnerability to invasion; and 5) there are several links among carrying capacity, ecosystem states, and ecosystem stability.

Conclusions Overall, the many and varied definitions of carrying capacity, typically stated in rather vague and ambiguous terms, render the concept to be most useful in theoretical ecology. Efforts to parametrize and measure carrying capacity in the field have proven problematic, such that the practical utility of the concept is questionable. This dilemma is especially true when considering the worldwide carrying capacity of humans, which seems better approached by the concept of ecological footprint. Nonetheless, the carrying capacity concept is clearly of heuristic value given the fundamental truth that no population can grow without limit, and especially given the fact that many human societies have behaved as if no limits exist.

Source: Alan Beeby and Anne-Maria Brennan

Ecotourism/ Wildlife tourism in forest Wildlife is one of the components of biodiversity. It is a general term that technically covers both flora and fauna, although this document will cover fauna only. In popular use, wildlife mostly refers to animals in the wild. Perhaps a classic image of wildlife for many people is a large mammal or a flock of wild birds, but the term is widely used to cover all types of animals, including all kinds of insects and marine life (Tapper, 2006). The World Tourism Organization (UNWTO) defines tourism as a social, cultural and economic phenomenon which entails the movement of people to countries or places outside their usual environment for personal or business/professional purposes. A tourist is a traveller taking a trip to a main destination outside his/her usual environment, for less than a year, but for more than one day. A more common understanding of tourism is travelling for leisure or sightseeing. “Wildlife tourism” encompasses all forms and scales of tourism that involve the enjoyment of natural areas and wildlife. Wildlife tourism can be defined loosely as tourism that includes, as a principle aim, the consumptive and non-consumptive use of wild animals in natural areas. It may be high volume mass tourism or low volume/low impact tourism, generate high economic returns or low economic returns, be sustainable or unsustainable, domestic or international, and based on day visits or longer stays (Roe, D. et al., 1997). It is necessary to distinguish between wildlife tourism and ecotourism, as the terms are often used interchangeably. The International Ecotourism Society defines ecotourism as “responsible travel to natural areas that conserve the environment and improve the well-being of local people”. Ecotourism focuses on experiencing wildlife in its natural environment. Although the goal of ecotourism is to enjoy nature, not all tourism in natural areas is sustainable and can be defined as ecotourism. An official global ecotourism certification scheme remains to be developed, but most agree that ecotourism should possess qualities such as minimal impact to the natural environment, sensitivity and enhanced awareness of local environments and cultures, financial support for local conservation initiatives, and empowerment and participation of local communities. “Wildlife watching” is simply an activity that involves watching wildlife. It is normally used to refer to watching animals, and this distinguishes wildlife watching from other forms of wildlife-based activities, such as hunting and fishing. Watching wildlife is essentially an observational activity, although it can sometimes involve interactions with the animals being watched, such as touching or feeding them. Wildlife watching tourism is tourism that is organized and undertaken in order to watch wildlife. This type of has grown dramatically in recent years; a quick search on the internet provides many examples of tourism companies that either market specific wildlife watching tours, or promote their products by highlighting wildlife watching as an optional activity that their clients can enjoy. The tourism industry tends to use the term “wildlife tourism” rather than wildlife watching tourism. In many instances, the two terms are identical, but wildlife tourism is sometimes also used to refer to hunting or fishing tourism and, in a few cases, refers to viewing captive wildlife in zoos or confined parks. Wildlife tourism is an element of many nations' travel industry centered around observation and interaction with local animal and plant life in their natural . While it can include eco- and animal-friendly tourism, safari hunting and similar high-intervention activities also fall under the umbrella of wildlife tourism. Wildlife tourism, in its simplest sense, is interacting with wild animals in their natural habitat, either by actively (e.g. hunting/collection) or passively (e.g. watching/photography). Wildlife tourism is an important part of the tourism industries in many countries including many African and South American countries, Australia, India, Canada, Indonesia, Bangladesh, Malaysia, Sri Lanka and Maldives among many. It has experienced a dramatic and rapid growth in recent years worldwide and many elements are closely aligned to eco-tourism and sustainable tourism. As a multimillion-dollar international industry, wildlife tourism is often characterized by the offering of customized tour packages and safaris to allow close access to wildlife.

Description Wildlife tourism mostly encompasses non-consumptive interactions with wildlife, such as observing and photographing animals in their natural habitats. It also includes viewing of and interacting with captive animals in zoos or wildlife parks, and can also include animal-riding (e.g. elephant riding) and consumptive activities such as fishing and hunting, which will generally not come under the definition of ecotourism and may compromise animal welfare. It has the recreational aspects of adventure travel, and usually supports the values of ecotourism and nature conservation programs.  Negative impacts Wildlife tourism can cause significant disturbances to animals in their natural habitats. Even among the tourism practices which boast minimal-to-no direct contact with wildlife, the growing interest in traveling to developing countries has created a boom in resort and hotel construction, particularly on rain forest and mangrove forest lands. Wildlife viewing can scare away animals, disrupt their feeding and nesting sites, or acclimate them to the presence of people. In Kenya, for example, wildlife-observer disruption drives cheetahs off their reserves, increasing the risk of inbreeding and further endangering the species. The practice of selling slots for tourists to participate in sanctioned hunts and culls, though seemingly innocent, can serve to impact populations negatively through indirect means. Though culls can and do serve a crucial role in the maintenance of several ecosystems’ health, the lucrative nature of these operations lends itself to by unofficial groups and/or groups which are not fully aware of the potential negative impact of their actions. This is especially true of big-game and highly marketable species. Such unofficial organizations can promote the hunting or collecting of wildlife for profit without participating in or being sanctioned by wildlife management authorities while mimicking organized operations to fool unwary tourists. Though not sanctioned by any authority, the fact that these operations are funded by tourists and fueled by wildlife classifies such illicit hunting activity as “wildlife tourism”. Direct impacts The impacts wildlife tourism will have on wildlife depends on the scale of tourist development and the behavior and resilience of wildlife to the presence of humans. When tourists activities occur during sensitive times of the life cycle (for example, during nesting season), and when they involve close approaches to wildlife for the purpose of identification or photography, the potential for is high. Not all species appear to be disturbed by tourists even within heavily visited areas. Disturbing breeding patterns The pressures of tourists searching out wildlife to photograph or hunt can adversely affect hunting and feeding patterns, and the breeding success of some species. Some may even have long-term implications for behavioral and ecological relationships. For example, an increase in boat traffic has disturbed the feeding of giant otters in Manú National Park, Peru. Further disturbance to wildlife occurs when tourist guides dig up turtle nests and chase swimming jaguars, tapirs, and otters to give clients better viewing

opportunities. On the shores of Lake Kariba in Zimbabwe, the number of tourist boats and the noise generated has disrupted the feeding and drinking patterns of elephants and the black rhinoceros - it is feared that further increases in boat traffic will affect their reproductive success. The disturbance caused by human intervention may prevent species from their regular breeding and feeding activities. Disturbing feeding patterns Artificial feeding of wildlife by tourists can have severe consequences for social behavior patterns. Artificial feeding by tourists caused a breakdown of the territorial breeding system of land iguanas on the South Plaza in the Galápagos Islands. Territories were abandoned in favor of sites where food could be begged from tourists, and this has had a negative effect on the breeding success of iguanas. Artificial feeding can also result in a complete loss of normal feeding behaviors. In the Galápagos Islands, overfeeding by tourists was so extreme that, when stopped, some animals were unable to locate their natural food sources. Similarly, until the early 1970s, the diet of some grizzly bears in Yellowstone National Park consisted, to a large extent, of food wastes left by visitors at park refuse sites. When these sites were closed, the bears showed significant decreases in body size, reproductive rate, and litter size. Distruption of parent-offspring bonds Wildlife tourism also causes disruption to intra-specific relationships. Attendance by female harp seals to their pups declined when tourists were present and those females remaining with their pups spent significantly less time nursing and more time watching the tourists. There is also a risk of the young not being recognized, and being more exposed to predator attacks. A similar concern has been expressed over whale watching, whale calves normally maintain constant body contact with their mothers but, when separated, can transfer their attachment to the side of the boat. Increased vulnerability to predators and competitors The viewing of certain species by wildlife tourists makes the species more vulnerable to predators. Evidence of this phenomenon has been recorded in birds, reptiles and mammals. Problems have occurred in breeding colonies of pelicans. Increased mortality, vanity hunts, and poaching Vanity hunts (also called canned hunts) tend to breed their animals for specific desirable features without regard for the genetic health of the population. Breeding efforts can incorporate elements of inbreeding as specific features are aggressively sought. Inbreeding not only reinforces the presence of desirable features but brings with it the risk of inbreeding depression, which can reduce population fitness. Such operations also tend to feature other forms of animal abuse including inadequate housing and improper diet. Poaching, similarly to vanity hunting, selects strongly for animal phenotypes deemed desirable by hunters. This “harvest selection” (sometimes termed “unnatural selection”[7]) for specific human- desired features depletes natural populations of alleles which confer those desirable phenotypes. Often, these features (large horns, large size, specific pelts) are not only desirable to humans, but play roles in survival within the animal’s natural habitat and role within their ecosystem. By cutting down the number of animals bearing those desired phenotypes (and thus harboring the associated alleles), the amount of genetic material necessary for conferring those phenotypes upon later generations of the population is depleted (an example of genetic drift). This selection changes population structure over time, and can lead to a decrease in the wild-condition fitness of the population as it is forced to adapt around hunting-condition pressures.  Positive impacts Habitat restoration by eco-lodges and other tourism operations Many owners of eco-accommodation or wildlife attractions preserve and restore native habitats on their properties. In a large way, the tourists and travellers visiting the wildlife destinations contribute to the conservation and improvement of the conditions for the animals. The flow of the people keeps the poachers at bay from killing the valuable animals. The local tribes have a decent living as the tourism flourishes as it provides opportunities of improved livelihood. Conservation breeding Many wildlife parks (e.g. David Fleay Wildlife Park, Gold Coast, Australia) and zoos breed rare and endangered species as a part of their activities, and release the progeny when possible into suitable habitat.

Financial donations Some wildlife tourism contributes monetary donations to conservation efforts e.g. Dreamworld, Gold Coast, has a display of Sumatran tigers, and money from visitor donations and from their 'tiger walk' goes to Sumatra to assist in-situ conservation of wild tigers. Quality interpretation A good wildlife guide will impart a deeper understanding of the local wildlife and its ecological needs, which may give visitors a more informed base on which to subsequently modify their behaviour (e.g. not throw out plastic bags that may be eaten by turtles) and decide what political moves to support. Culls and Population Maintenance In order to provide for less invasive wildlife tourism features and maintain , wild populations occasionally require maintenance measures. These measures can include the aforementioned conservation breeding programs to bolster population numbers, or culls to reduce population numbers. Population reduction via culls occurs not only through the obvious means of direct (fatal) removal of individuals, but by implementing an additional selective pressure upon the population. This “harvest selection” can alter allelic frequency (a measure of genetic diversity, and thus related to genetic health) within a population, allowing the hunters to shape future generations by hunting the current. Conservation Hunting/Harvest "Well monitored trophy hunting is inherently self-regulating, because modest off-take is required to ensure high trophy quality and thus marketability of the area and future seasons". For example in Zimbabwe trophy hunting was largely responsible for the conversion of 27,000 km2 of livestock ranches to game ranching and a subsequent quadrupling of wildlife populations. In South Africa there are approximately 5000 game ranches and 4000 mixed livestock/game ranches with a population of >1.7 million wild animals, presently 15-25% of ranches are used for wildlife production Anti-poaching Bringing tourists regularly into some areas may make it more difficult for poachers of large animals or those who collect smaller species for the black market. Some examples of tourism having a positive effect towards anti-poaching, are that of non-consumptive wildlife tourism services which in turn provide for economic benefit of rural communities, and also by providing these same local communities with game meat harvested through tourist activities such as hunting. Barrett and Arcese (1998) show that generating money sources from these non-consumptive practices of tourism generate a positive income effect and decrease game meat consumption while lowering illegal hunting (poaching).

Why Wildlife tourism? Wildlife is one of the most important resources provided by forest ecosystems. In the tropics alone, hunting is an ubiquitous activity on which 200-300 million forest dwelling people are directly dependent for part or all of their livelihood and food. However, the abundance of wildlife has declined in many tropical forest areas, which jeopardizes the nutritional base on

which local communities depend, and threatens the ecological integrity of the tropical forests. Given the importance of wildlife resources, the implementation of sustainable management approaches is thus an imperative issue. Wildlife is also important in tourism. In tropical forests, rare, dangerous, or colorful animals represent a major travel motive, even though the significance of these forests for recreation, education, and experiences is now growing in general. Wildlife habitat and species around the world are facing a crisis. It is estimated that global warming may cause the extinction of 15–37% of species by 2050. This is another aspect which needs attention because we could lose about 1.25 million species. Unlike other environmental losses, this one cannot be reversed because nature does not give second chances to biodiversity. If we take into consideration the conventional reasons why wildlife is disappearing in Asia, India is doing far better than other countries. India has launched an extensive protected area network of research institutions in which legislation, socio-economic factors, and wildlife research are playing a great role. The Central Zoo Authority plays a key role with zoos in programming research activities related to the conservation and propagation of wild animals. Planned research activities include studies on wildlife biology, genetic variability, species- specific nutritional requirements, animal behavior, epidemiological surveys, and disease diagnosis through postmortem examination. The future depends on interaction between captive and wild animals, preservation of biodiversity, and genetic and demographic variations of species. India still has 65% of Asia’s tiger population, 85% of the Asian rhino population, 80% of the Asian elephant population, and 100% of the Asiatic lion population. These are all highly endangered and poached animals Introduction to Wildlife Tourism in India: India is the seventh largest country in the world and Asia’s second largest nation with an area of 2 3,287,263 km , a national border of 15,200 km, and a coastline of 7516 km. Ecologically, India can be divided into three main regions: • the Himalayan Mountain system; • the peninsular India subregion (woodlands and desert); and • the tropical rain forest region. A great wealth of biological diversity exists in these regions and in India’s wetlands and marine areas. This richness is shown in absolute numbers of species and the proportion of the world’s total they represent (Table 1). India is one of the world’s ‘mega diversity’ countries. It is ranked ninth in the world in terms of higher plant . At the ecosystem level, India is also well-endowed, with ten distinct biogeographic zones. It also contains four of the world’s 25 biodiversity hotspots, because of their extraordinarily high levels of species-richness and endemicity, and threatened status.

India is a land of most beautiful wild lands and natural parks, rich in bio-diversity and heavily populated forests. At present, there are 870 National Parks, Wildlife Sanctuaries

and protected areas in the country (June, 2019). Some 3000 most beautiful natural areas and wild lands are known for their scenic beauty. These can be used just to encourage wildlife tourism and natural tourism in the country. At present 6.5 million tourists are visiting India annually and most of them are wild life tourists or tourists interested to visit natural areas. Wildlife protection and conservation activities should be encouraged to boost up wildlife tourism. There is a great need to encourage conservation work through creating natural habitats, expanding the park area, stopping deforestation and encroachment by farmers, pastoral people and timber smugglers. After creating a peaceful and pleasant environment, the tourism should be encouraged at a larger scale. There is some impact of tourism but it can be overcome by some skillful ways of park authorizes and staff. The people of the Indian subcontinent were once blessed with some of the most profuse natural gifts: verdant forests, water-stocked Himalayan ranges, rich coastal fish resources, productive estuaries, grassy pastures, and bountiful river systems. Abundant rain and fertile soils added to this plentitude. Years of mismanagement, however, have degraded our forests, wounded our coastline, and poisoned our aquifers with devastating results. Today, India contains 172 species (2.9% of the world’s total number) of animals that are considered to be globally threatened by the IUCN. These include 53 species of mammals, 69 species of birds, 23 species of reptiles, and 3 species of amphibians. Extinction is somehow classified as ‘biological reality’ because no species has, as yet, existed for more than a few million years without evolving into something different or dying out completely. Extinction is threatening all species, but most of the time smaller animals, like bats and rodents, face this threat more than other animals. We, however, tend to focus on the charismatic , which we like to see and which fascinate us. Success in evolution is measured in terms of survival: failure, by extinction. Most recent extinctions can be attributed, either directly or indirectly, to human demographic and technological expansion, commercialized exploitation of species, and human-caused environmental change. These factors, in turn, have affected the reproductive rate of endangered species and their adaptability to changing environmental conditions. Concern for wildlife is, in fact, a concern for ourselves. GOOD PRACTICE ON WILDLIFE CONSERVATION AND TOURISM: Sustainable tourism does not happen by itself. In fact, several factors can work against sustainability. The needs of tourists, for instance, are different from those of local residents, and planners may tend to prioritize the expectations of customers. Competition for resources between locals and tourists may cause inflation and overexploitation of resources. Sustainable tourism is about site or destination plans, and tourism policies and strategies that reflect the ways and means of achieving the goals and milestones for sustainability. Policies often defer to institutional set-ups that allow governance of tourism development. Policies may not be site specific and may apply across all of a country’s area, whereas strategies are more action oriented and are often linked to a destination or region. Policies and strategies describe a future desired state (vision) and detail the necessary steps to achieve that vision. Although governments are essential in moderating negotiations between different interest groups, it is important to have a consistent interrelationship between different policies and strategies (tourism, poverty reduction and biodiversity). To achieve sustainable tourism, tools that can be used include tourism policies, inter-ministerial and inter-agency corporation mechanisms, partnerships that allow park agencies to work with industry and retain parts of revenue for conservation and local development, and training for professionals and communities. Appendix 1 (Planning process) suggests that auditors utilize the CBD Guidelines on Biodiversity and Tourism Development and its User’s Manual as references in their sustainable tourism planning process. The Guidelines ask questions about the use of regional/global standards, guidelines and principles, and global criteria. Significance of wildlife tourism: In modern times nature tourism and wildlife tourism is attracting the foreign tourists at larger scale. The scenic spectrum of natural areas is always attracting the lovers of nature. The amazing wild animals are a great source of human recreation. In several countries wildlife tourism has become the backbone of their economy. There is great need to

encourage wildlife tourism in India as it has a rich and varied wildlife in the forests. By encouraging wildlife tourism, it will pave the way for wildlife conservation thus creating a mass awareness among the people of the country. Wildlife tourism confer • Minimize impact on the environment • Build environmental and cultural awareness and respect • Provide positive experiences for both visitors and hosts • Provide direct financial benefits for conservation • Provide financial benefits and empowerment for local people • Raise sensitivity to host countries' political, environmental, and social climate.  Minimize impact on the environment Business or industry that occurs without damage or causing change to the environment is often described as sustainable, because it can keep going without any negative impact on the environment or natural resources, and without depleting natural resources.  Build environmental and cultural awareness and respect This means to make people, both tourists and those who live and work in the area, more knowledgeable of local environmental and cultural issues and to promote behaviours that are sympathetic to local traditions and environment. Provide positive experiences for both visitors and hosts The presence of tourists and tourism should not be detrimental to the local population, equally the host communities should not cause problems for the visitors. Provide direct financial benefits for conservation Tourism should generate money, through taxes or otherwise, that supports the cost of conservation. Provide financial benefits and empowerment for local people, also referred to as ‘Improving the well-being’, means making people’s lives better in one way or another. There are many ways in which touristic activity in an area can improve local people’s lives – pride from knowing that people in faraway places want to visit and know about their area makes people feel good; we learn all sorts of things from meeting and seeing visitors from different places. Tourism brings many other related activities, support services, a supply industry and so on. A key issue is ensuring that benefits are felt by the local people. In 2004 the UNWTO (The World Tourism Organization is the United Nations specialized agency) listed six elements required to enable the economic benefits of tourism to reach the local populations: 1. Employment in tourism enterprises; 2. Supply of goods and services to tourism enterprises by the local populations or by enterprises employing locals; 3. Direct sales of goods and services to visitors by the local populations; 4. Tax or levy on tourism income or profits, with proceeds benefiting the local population; 5. Voluntary giving/support by tourism enterprises and tourists; 6. Investment in infrastructure and social services stimulated by tourism that also benefit the local , directly or through support to other sectors. This is more or less the same as ‘Sustainable tourism,’ as defined by the UNWTO - Sustainable tourism should: • Make optimal use of environmental resources, maintaining essential ecological processes and helping to conserve natural heritage and biodiversity; • Respect the socio-cultural authenticity of host communities, conserve their built and living cultural heritage and traditional values and contribute to intercultural understanding and tolerance; • Ensure viable, long-term economic operations, providing socio-economic benefits to all stakeholders that are fairly distributed, including stable employment and income-earning opportunities and social services to host communities and contributing to poverty alleviation.

Concept of Climax Persistance is the process of change in the species structure of an ecological community over time. The entire process of succession completed through nudation, invasion, competition and coaction, reaction and stabilization. After the completion of those process the pioneer community (first appear) transformed to through different seral community. Once the climax community has established itself, its general appearance does not change in spite of the constant replacement of individuals within the community. However, all climaxes do not persist for ever. A stable climax community is not possible for long, as natural disturbances like storms; fire, cold waves, season etc. have detrimental effects. Clements believe that succession resulted in a single true climax community that was determined primarily by the climate of the region- this view is called monoclimax theory of succession. But Tansley’s polyclimax theory suggest and recognized the validity of many different types of vegetation as climax which are depends on local population. More recently, the development of the continuum index and gradient analysis fostered the broader climax-pattern theory of Robert Whittakar, which recognizes a regional pattern of open climax community whose composition at any one locality depends on the particular environment conditions at that point. Non- successional, short term, reversible changes in the floristic and faunal composition (or fluctuations) of a community are also common. These, are said to be cases of transient climax. Transient climaxes develop on ephemeral resources and habitats such as temporal ponds and carcases of animals. The development of animal and plant communities in seasonal ponds is a simple case of transient climax. Pond waters either dry up in summer or freeze solid in winter, thereby regularly destroying the communities. These communities re-establish each year during the growing season from the pores and resting stages left by plants, animals and . Another example is the excreta and carcasses of dead organisms. They are resources for a wide variety of feeders and scavengers. The dead body of a large animal is fed upon by a succession of vultures in African savannas. First, the large, aggressive species eats the largest masses of flesh, followed by smaller species that picks smaller bits of meat from the bones. Finally, another kind of vulture invades the area that cracks open the bones and feeds on the bone marrow. Later scavenger mammals, maggots, micro-organisms enter the area and ensure that nothing edible remains. When the feast is concluded all the scavengers disperse. Thus, no climax is present in this sort of succession or we may consider all the scavengers as a part of a climax. A few dominant species in a few simple communities may create a cyclic climax. Cyclic climax develops where each species become established only in association with some other species. The change in cyclic pattern occurs due to the life cycle of dominant species. Stable cyclic climaxes usually follow a cyclic pattern often with one of the stages being bare substrate. Harsh physical conditions, such as frost, strong winds etc. result in cyclic climaxes. Examples of cyclic vegetation changes was studied by Watt (1947). Watt found that the dwarf Calluna heath in Scotland was the dominant shrub. It looses its vigor as it ages and is invaded by the lichen, Cladonia. The lichen mat dies in time to leave bare ground. This bare area is invaded by bearberry (Arctostaphylos). It is, in turn, invaded by Calluna. Calluna is the dominant plant, while Arctostaphylos and Cladonia are allowed to occupy the area that is temporarily vacated by Calluna. Thus, the life history of this dominant plant controls the cyclic sequence:

The concept of climax community incorporates cyclic patterns of change and mosaic patterns of distribution. The climax is a dynamic and self-everlasting state. Persistence is the key to climax. In a climax community, all species (including dominant species), are continually able to reproduce successfully and persists in a uniform climatic area.

Persistence refers to the tendency of populations to remain within acceptable limits of size despite disturbance. Persistence determine the relative timing of species’ appearance in, and disappearance from, the community. In areas where the poor competitors arrive first, become established and are subsequently invaded by a better competitor, their populations are significantly reduced, but the species is able to persist in the community. However, if the better competitor arrives first, the less competitive species are unable to invade the community and are therefore excluded (Drake, 1991). The minimum area in which a population or community is stable and/or persistent can be define as the smallest area that provides adequate conditions (i.e., enough propagules and the environmental conditions required for the development, growth, and survival of offspring) for the replacement of existing adults somewhere within. However in case of scenario envisions a species persisting in a network of habitat patches through a balance between frequent local (within-patch) extinctions and recolonizations.

Persistence enhancing propensity (PEP) account of role functions in ecology. According to our proposed PEP account, ecological function may be defined as such: The function of x in an ecosystem E is to F if, and only if, x is capable of doing F and x’s capacity to F contributes to E’s propensity to persist. The shift from survival to persistence is not trivial given that survival is an organism-centric concept. But more importantly, because persistence is more genuinely time-comparison relative, one should not focus exclusively on the maintenance of the stability of a given system defined as its ability to return to its equilibrium state after disturbance. Some ecologist emphasis on over engineering resilience (stability), and proposed that ecological functions should be defined relative to an ecosystem’s more general ability to persist, often by “tolerating” and “absorbing” change, given a succession of different states on different temporal scales (more on this below). Thus, there is link between the notion of ecological function to the ahistorical concept of evolutionary adaptation and central to “extended adaptationist” approaches to evolution like the and extended organism perspectives. So, a strong analogy between the fitness of organisms understood in terms of survival and reproduction and the adaptiveness of ecosystems understood as their potential to persist (often referred to in ecology as their resilience). How long a community persists can be controlled by planned removal, which deliberately interrupts a successional sequence. The removal process can, in itself, be considered a type of disturbance, and can be used to regulate subsequent successional sequences and rates of replacement. In some instances a regenerating community is the goal, and management efforts can be adjusted to prevent successional sequences from occurring. The model consists of five steps: (1) designed disturbance, (2) selective colonization, (3) inhibitory persistence, (4) removal, and (5) regeneration (Fig. 6). The management of a specific area first involves designing a disturbance that alters community structure in ways which can eliminate competitors and enhance the ecesis and survival of introduced, indigenous colonizers. The species and population sizes of colonizers are selected to influence subsequent patterns of community development. The length of time which a community persists can be manipulated by using one or more of several possible planning techniques. Management objectives determine whether the successional sequence terminates, in a removal process (such as a selective harvest), or is extended through regeneration.

Fig.6. The model consists of five steps: (1) designed disturbance, (2) selective colonization, (3) inhibitory persistence, (4) removal, and (5) regeneration

Theoretical approaches to climax persistence: If highly interactive ecological communities are susceptible to biotic feedback instabilities and if weakly interactive ecological communities are prone to stochastic extinctions, what enables a community of species to persist in an ecosystem over the course of time? Beginning in the 1970's a great amount of effort has been expended on this problem. The resultant ecological models addressed the problem in two general ways: (1) they incorporated stabilizing mechanisms into basic classical models that could preserve the stability of equilibrium states, or (2) they abandoned the stable equilibrium state as a fundamental property at the local scale and examined mechanisms ensuring long- term persistence of communities. Persistence refers to the tendency of populations to remain within acceptable limits of size despite disturbances. These two responses to the problem are quite different in spirit and, although we will discuss both below, the second has seemingly opened up richer areas for investigation than the first. The models that can be classified as following approach (2) are very diverse, but we believe that nearly all of them can be encompassed within the scheme represented in the diagrams in Fig. 7a, b, c, d. The diagrams in Fig. 7 depict spatial regions in an abstract sense, though the property of spatial extent is crucial only in cases (a) and (d). In models classed under (a) it is assumed that biotic forces dominate and are strong enough to cause feedback instabilities and extinctions. However, the community is separated into weakly or occasionally coupled spatial subregions that are

generally out of phase dynamically. Community instabilities in one subregion will not affect others. Subregions (these will also be called "cells" or patches, especially in discussing models) depleted of some species by feedback instabilities can be recolonized later from other subregions. Models of type (b) are also dominated by unstable biotic feedback interactions. The factor that prevents extinctions in this case is not spatial quasi- isolation, but a stochastic disturbance regime that pre- vents biotic forces from operating continuously to the point where they cause extinctions. In Fig. 4c the system is considered to be largely stochastically dominated, but biotic forces are assumed to be strong and compensatory in critical instances. For example, biological populations may show high resistance to further reduction when at low levels, though the populations show no signs of having equilibrium points. Cases (b) and (c) are in some sense symmetric. In case (b) biotic is moderated by a disturbance regime, whereas in case (c) stochastic dominance is moderated by compensatory biotic forces at key times. Lastly, models in class (d) assume stochastic dominance that would cause extinction. How- ever, the stochastic disturbances act at spatial scales smaller than those occupied by the biotic community, affecting different subregions, or cells, at different times Extinctions in one cell can be made up for by immigration from other cells. Case (d) resembles case (a) in representing a heterodemic rather than a pandemic view of communities, but stochastic dominance takes the place of biotic feedback instability in causing transient behavior on the small spatial scale.

Fig.7. Four mechanisms proposed for increasing the per- sistence of ecological systems: (a) biotic feedback instabilities are localized to subpopulations, which can be replenished by subsequent colonization; (b) disturbances prevent feedback instabilities (competitive exclusion, etc.) from eliminating species; (c) strong biotic compensatory forces act at low pop- ulation densities to enable remnant populations to survive severe disturbances; (d) harmful environmental disturbances occur out of phase spatially, so that some subpopulations survive and recolonize depopulated areas.

However, nearly all models that have attempted to deal with the long-term survival (persistance) of ecological communities can be classified as one of the types described briefly above, or perhaps as a combination of these types. Below, by discussing a variety of notable models. Fig. 8 puts these into a visual framework.

Fig. 8

Does ecological succession ever stop?

There is a concept in ecological succession called the "climax" community. The climax community represents a stable end product of the successional sequence. In the climate and landscape region of the Nature Trail, this climax community is the "Oak-Poplar Forest" subdivision of the Deciduous Forest Biome. An established Oak-Poplar Forest will maintain itself for a very long period of time. Its apparent species structure and composition will not appreciably change over observable time. To this degree, we could say that ecological succession has "stopped". We must recognize, however, that any ecosystem, no matter how inherently stable and persistent, could be subject to massive external disruptive forces (like fires and storms) that could re-set and re-trigger the successional process. As long as these random and potentially catastrophic events are possible, it is not absolutely accurate to say that succession has stopped. Also, over long periods of time ("geological time") the climate conditions and other fundamental aspects of an ecosystem change. These geological time scale changes are not observable in our "ecological" time, but their fundamental existence and historical reality cannot be disputed. No ecosystem, then, has existed or will exist unchanged or unchanging over a geological time scale.

All living systems, from a cell to the biosphere (Fig. 9), maintain some degree of sustainability or stability by constantly changing in response to changing environmental conditions. It is useful to distinguish among three aspects of stability or sustainability in living systems. One is inertia, or

persistence: the ability of a living system to resist being disturbed or altered. A second is constancy: the ability of a living system such as a population to keep its numbers within the limits imposed by available resources. A third factor is resilience: the ability of a living system to repair damage after an external disturbance that is not too drastic. These three factors are discuss below:

Fig. 9. All living system. An ecosystem is said to possess (or equilibrium) if it is capable of returning to its equilibrium state after a perturbation (a capacity known as resilience) or does not experience unexpected

large changes in its characteristics across time. Although the terms community stability and ecological stability are sometimes used interchangeably, community stability refers only to the characteristics of communities. It is possible for an ecosystem or a community to be stable in some of their properties and unstable in others. For example, a vegetation community in response to a drought might conserve biomass but lose biodiversity. Stable ecological systems abound in nature, and the scientific literature has documented them to a great extent. Scientific studies mainly describe grassland plant communities and microbial communities. Nevertheless, it is important to mention that not every community or ecosystem in nature is stable. Also, noise plays an important role on biological systems and, in some scenarios, it can fully determine their temporal dynamics. The concept of ecological stability emerged in the first half of the 20th century. With the advancement of theoretical ecology in the 1970s, the usage of the term has expanded to a wide variety of scenarios. This overuse of the term has led to controversy over its definition and implementation. In 1997, Grimm and Wissel made an inventory of 167 definitions used in the literature and found 70 different stability concepts. One of the strategies that these two authors proposed to clarify the subject is to replace ecological stability with more specific terms, such as constancy, resilience and persistence. In order to fully describe and put meaning to a specific kind of stability, it must be looked at more carefully. Otherwise the statements made about stability will have little to no reliability because they would not have information to back up the claim. Following this strategy, an ecosystem which oscillates cyclically around a fixed point, such as the one delineated by the predator-prey equations, would be described as persistent and resilient, but not as constant. Some authors, however, see good reason for the abundance of definitions, because they reflect the extensive variety of real and mathematical systems. Stability analysis: When the species abundances of an ecological system are treated with a set of differential equations, it is possible to test for stability by linearizing the system at the equilibrium point. Robert May developed this stability analysis in the 1970s which uses the Jacobian matrix. Types: Although the characteristics of any ecological system are susceptible to changes, during a defined period of time, some remain constant, oscillate, reach a fixed point or present other type of behavior that can be described as stable. This multitude of trends can be labeled by different types of ecological stability. Dynamical stability: Dynamical stability refers to stability across time.  Stationary, stable, transient, and cyclic points: A stable point is such that a small perturbation of the system will be diminished and the system will come back to the original point. On the other hand, if a small perturbation is magnified, the stationary point is considered unstable.  Local and global stability Local stability indicates that a system is stable over small short-lived disturbances, while global stability indicates a system highly resistant to change in species composition and/or dynamics.  Constancy Observational studies of ecosystems use constancy to describe living systems that can remain unchanged. Resistance and inertia (persistence): Resistance and inertia deal with a system's inherent response to some perturbation. A perturbation is any externally imposed change in conditions, usually happening in a short time period. Resistance is a measure of how little the variable of interest changes in response to external pressures. Inertia (or persistence) implies that the living system is able to resist external fluctuations. In the context of changing ecosystems in post-glacial North America, E.C. Pielou remarked at the outset of her overview, "It obviously takes considerable time for mature vegetation to become established on newly exposed ice scoured rocks or glacial till...it also takes considerable time for whole ecosystems to change, with their numerous interdependent plant species, the habitats these create, and the animals that live in the

habitats. Therefore, climatically caused fluctuations in ecological communities are a damped, smoothed-out version of the climatic fluctuations that cause them. Resilience, elasticity and amplitude: Resilience is the tendency of a system to retain its functional and organizational structure and the ability to recover after a perturbation or disturbance. Resilience also expresses the need for persistence although from a management approach it is expressed to have a broad range of choices and events are to be looked at as uniformly distributed. Elasticity and amplitude are measures of resilience. Elasticity is the speed with which a system returns to its original / previous state. Amplitude is a measure of how far a system can be moved from the previous state and still return. Ecology borrows the idea of neighborhood stability and a domain of attraction from dynamical systems theory.  Lyapunov stability Researchers applying mathematical models from system dynamics usually use Lyapunov stability.  Numerical stability Focusing on the biotic components of an ecosystem, a population or a community possesses numerical stability if the number of individuals is constant or resilient.  Sign stability It is possible to determine if a system is stable just by looking at the signs in the interaction matrix. Structural stability:  Stability and diversity The relation between diversity and stability has been widely studied. Diversity can operate to enhance the stability of ecosystem functions at various ecological scales. For example, genetic diversity can enhance resistance to environmental perturbations. At the community level, the structure of food webs can affect stability. The effect of diversity on stability in food-web models can be either positive or negative, depending on the trophic coherence of the network.[16] At the level of landscapes, environmental heterogeneity across locations has been shown to increase the stability of ecosystem functions  History of the concept The term 'oekology' was coined by Ernst Haeckel in 1866. Ecology as a science was developed further during the late 19th and the early 20th century, and increasing attention was directed toward the connection between diversity and stability. Frederic Clements and Henry Gleason contributed knowledge of community structure; among other things, these two scientists introduced the opposing ideas that a community can either reach a stable climax or that it is largely coincidental and variable. Charles Elton argued in 1958 that complex, diverse communities tended to be more stable. Robert MacArthur proposed a mathematical description of stability in the number of individuals in a food web in 1955. After much progress made with experimental studies in the 60's, Robert May advanced the field of theoretical ecology and refuted the idea that diversity begets stability. Many definitions of ecological stability have emerged in the last decades while the concept continues to gain attention. ………….

Ecology of perturbance In ecological studies, the two concepts ‘perturbation’ and ‘stress’ are often used synonymously to disturbance. Processes and mechanisms that are generally described as disturbance may instead be classified as either perturbation or stress, and the terms perturbation and stress are often used interchangeably with disturbance without explicitly definitions of any of the terms. Similarly, the term perturbation can be used to refer to the effects of stress on a system and the term stress can be used to describe a perturbation (Odum et al. 1979). That these three terms are used haphazardly can be problematic, because definitions of ecological phenomena may be vital for experimental design in tests of hypotheses. Especially, since the concept of disturbance is in itself a quagmire, confounding it with stress or perturbation would be severely suboptimal. Rykiel (1985) defines perturbation as “the response of an ecological component or system to disturbance or other ecological process as indicated by deviations in the values describing the properties of the component or system; relative to a specified reference condition; characterized by direction, magnitude, and persistence”. Hence, according to Rykiel (1985) disturbance is the agent causing damage whereas perturbation, as well as stress, is the effects of a disturbance. Agents of perturbation are commonly similar to those of disturbance and stress, such as flood scouring, environmental variation, alteration of species densities. Moreover, the term unperturbed is used by Padisak (1993) to describe systems unaffected by either disturbance or stress. Another exception is the definition by Picket and White (1985), where perturbation is “a departure (explicitly defined) from a normal state, behaviour, or trajectory (also explicitly defined)”.

“For a ecosystem to be considered stable, there must exist one or more equilibrium points or limit cycles (1) at which the system remains when faced with a disturbing force or (2) to which it returns" after a perturbation has caused a significant change in structure. The first aspect of stability is most appropriately called resistance stability, since a force has been applied and resisted. The second aspect, return to equilibrium after being perturbed, is called adjustment stability. So, in ecological point of view perturbation is a force that actually causes a significant change in community structure. If the intensity of the disturbing force does not cause a significant change in the characteristic of interest, there is no perturbation; the assemblage has resisted the force. If the perturbation has no [significant] effect, i.e., the community is resistant to it, the only appropriate time scale is related to the perturbation frequency.... If the perturbation changes community structure [significantly], the time scale must include the relation between the perturbation frequency and the community response.

At the ecosystem level of organization, disturbances which affect individuals (for example, fire, treefall caused by wind) may appear to have no effect. That is, no perturbation is induced in ecosystem variables

or properties. However, a disturbance to an individual has certainly occurred and caused a perturbation. The effect of a disturbance depends on the organizational level used as a frame of reference, the scale at which the system is observed, and the ecological processes which can propagate the disturbance across levels at the specified scale. A disturbance at one level does not necessarily induce perturbations in all levels. Perturbations cause chronic changes (typically anthropogenic, but sometimes natural) push ecosystems to thresholds that cause collapse of process and function and may become permanent. Ecosystem resetting occurs when episodic natural disasters breach thresholds with little or no warning, resulting in long-term changes to environmental attributes or ecosystem function. Resilience addresses the ability of ecosystems to absorb change and disturbance and adapt to small- scale perturbations, both in the length of time it takes to recover from external stress and in the magnitude of stress from which a system can recover without rapidly moving to a new stable condition. While many resilience concepts evolved from ecology, resilience has relevance to other ecosystem characteristics, such as the sustainability of surface water and groundwater. Although perturbed ecosystems and components do not always return to the exact state before a disturbance, there is a recognized bound on the breadth of resilience: if a system is viewed as resilient, it is generally perceived as remaining within specified “bounds.” While this notion of an essentially finite system is accepted even by critics of sustainable development, the concepts of permanent ecosystem change are typically absent from sustainability discussions. When the system loses resilience it becomes vulnerable to perturbations that earlier could be absorbed without structural change (Gunderson et al., 1997). Resilience has been defined in very different ways, but mainly two connotations dominate the ecological literature. The most common definition is related to the capacity of ecological systems to recover from a disturbance (Walker, 1995). Under this point of view, resilience can be measured by how fast the variables of the system return to their equilibrium following a perturbation (Pimm, 1984; MacGillivray et al., 1995). The second definition (the most used in the literature) emphasises the existence of alternative states in ecosystems. Under this approach, resilience is the ability of the system to maintain its structure and patterns of behaviour in the face of disturbance, that is, the capacity to absorb perturbations and still persist (Holling, 1973, 1986). In this context, resilience can be measured by the magnitude of disturbance that can be absorbed before the system flips to another state — before an ecological threshold is reached.

In ecology, a disturbance is a temporary change in environmental conditions that causes a pronounced change in an ecosystem. Disturbances often act quickly and with great effect, to alter the physical structure or arrangement of biotic and abiotic elements. A disturbance can also occur over a long period of time and can impact the biodiversity within an ecosystem. Major ecological disturbances may include fires, flooding, storms, insect outbreaks and trampling. Earthquakes, various types of volcanic eruptions, tsunami, firestorms, impact events, , and the devastating effects of human impact on the environment (anthropogenic disturbances) such as clearcutting, forest clearing and the introduction of can be considered major disturbances. Not only invasive species can have a profound effect on an ecosystem, but also naturally occurring species can cause disturbance by their behavior. Disturbance forces can have profound immediate effects on ecosystems and can, accordingly, greatly alter the natural community. Because of these and the impacts on populations, disturbance determines the future shifts in dominance, various species successively becoming dominant as their life history characteristics, and associated life-forms, are exhibited over time. Criteria: Conditions under which natural disturbances occur are influenced mainly by climate, weather, and location. Natural fire disturbances for example occur more often in areas with a higher incidence of lightning and flammable biomass, such as longleaf pine ecosystems in the southeastern United States. Conditions often occur as part of a cycle and disturbances may be periodic. Other disturbances, such as those caused by humans, invasive species or impact events, can occur anywhere and are not necessarily cyclic. Extinction vortices may result in multiple disturbances or a greater frequency of a single disturbance. Immediately after a disturbance there is a pulse of or regrowth under conditions of little competition for space or other resources. After the initial pulse, recruitment slows since once an individual plant is established it is very difficult to displace. Due to the varying forms of disturbance this directly impacts the organisms which will exploit the disturbance and create diversity within an ecosystem.

Cyclic disturbance: Often, when disturbances occur naturally, they provide conditions that favor the success of different species over pre-disturbance organisms. This can be attributed to physical changes in the biotic and abiotic conditions of an ecosystem. Because of this, a disturbance force can change an ecosystem for significantly longer than the period over which the immediate effects persist. With the passage of time following a disturbance, shifts in dominance may occur with ephemeral herbaceous life-forms progressively becoming over topped by taller perennials herbs, shrubs and trees. However, in the absence of further disturbance forces, many ecosystems trend back toward pre-disturbance conditions. Long lived species and those that can regenerate in the presence of their own adults finally become dominant. Such alteration, accompanied by changes in the abundance of different species over time, is called ecological succession. Succession often leads to conditions that will once again predispose an ecosystem to disturbance. Pine forests in the western North America provide a good example of such a cycle involving insect outbreaks. The mountain pine beetle (Dendroctonus ponderosae) play an important role in limiting pine trees like lodgepole pine in forests of western North America. In 2004 the beetles affected more than 90,000 square kilometres. The beetles exist in endemic and epidemic phases. During epidemic phases swarms of beetles kill large numbers of old pines. This mortality creates openings in the forest for new vegetation. Spruce, fir, and younger pines, which are unaffected by the beetles, thrive in canopy openings. Eventually pines grow into the canopy and replace those lost. Younger pines are often able to ward off beetle attacks but, as they grow older, pines become less vigorous and more susceptible to infestation. This cycle of death and re-growth creates a temporal mosaic of pines in the forest. Similar cycles occur in association with other disturbances such as fire and windstorms. When multiple disturbance events affect the same location in quick succession, this often results in a "compound disturbance," an event which, due to the combination of forces, creates a new situation which is more than the sum of its parts. For example, windstorms followed by fire can create fire temperatures and durations that are not expected in even severe wildfires, and may have surprising effects on post-fire succession. Environmental stresses can be described as pressure on the environment, with compounding variables such as extreme temperature or precipitation changes—which all play a role in the diversity and succession of an ecosystem. With environmental moderation, diversity increases because of the intermediate- disturbance effect, decreases because of the competitive- exclusion effect, increases because of the prevention of competitive exclusion by moderate predation, and decreases because of the local extinction of prey by severe predation. A reduction in recruitment density reduces the importance of competition for a given level of environmental stress. Species adapted to disturbance: A disturbance may change a forest significantly. Afterwards, the forest floor is often littered with dead material. This decaying matter and abundant sunlight promote an abundance of new growth. In the case of forest fires a portion of the nutrients previously held in plant biomass is returned quickly to the soil as biomass burns. Many plants and animals benefit from disturbance conditions. Some species are particularly suited for exploiting recently disturbed sites. Vegetation with the potential for rapid growth can quickly take advantage of the lack of competition. In the northeastern United States, shade- intolerant trees like pin cherry and aspen quickly fill in forest gaps created by fire or windstorm (or human disturbance). Silver maple and eastern sycamore are similarly well adapted to floodplains. They are highly tolerant of standing water and will frequently dominate floodplains where other species are periodically wiped out. When a tree is blown over, gaps typically are filled with small herbaceous seedlings but, this is not always the case; shoots from the fallen tree can develop and take over the gap. The sprouting ability can have major impacts on the plant population, plant populations that typically would have exploited the tree fall gap get over run and can not compete against the shoots of the fallen tree. Species adaptation to disturbances is species specific but how each organism adapts effects all the species around them. Another species well adapted to a particular disturbance is the Jack pine in boreal forests exposed to crown fires. They, as well as some other pine species, have specialized serotinous cones that only open and disperse seeds with sufficient heat generated by fire. As a result, this species often dominates in areas where competition has been reduced by fire. Species that are well adapted for exploiting disturbance sites are referred to as pioneers or early successional species. These shade-intolerant species are able to photosynthesize at high rates and as a

result grow quickly. Their fast growth is usually balanced by short life spans. Furthermore, although these species often dominate immediately following a disturbance, they are unable to compete with shade-tolerant species later on and replaced by these species through succession. However these shifts may not reflect the progressive entry to the community of the taller long-lived forms, but instead, the gradual and dominance of species that may have been present, but inconspicuous directly after the disturbance. Disturbances have also been shown to be important facilitators of non-native plant invasions. While plants must deal directly with disturbances, many animals are not as immediately affected by them. Most can successfully evade fires, and many thrive afterwards on abundant new growth on the forest floor. New conditions support a wider variety of plants, often rich in nutrients compared to pre- disturbance vegetation. The plants in turn support a variety of wildlife, temporarily increasing biological diversity in the forest. Importance: Biological diversity is dependent on natural disturbance. The success of a wide range of species from all taxonomic groups is closely tied to natural disturbance events such as fire, flooding, and windstorm. As an example, many shade-intolerant plant species rely on disturbances for successful establishment and to limit competition. Without this perpetual thinning, diversity of forest flora can decline, affecting animals dependent on those plants as well. A good example of this role of disturbance is in ponderosa pine (Pinus ponderosa) forests in the western United States, where surface fires frequently thin existing vegetation allowing for new growth. If fire is suppressed, douglas fir (Pesudotsuga menziesii), a shade tolerant species, eventually replaces the pines. Douglas firs, having dense crowns, severely limit the amount of sunlight reaching the forest floor. Without sufficient light new growth is severely limited. As the diversity of surface plants decreases, animal species that rely on them diminish as well. Fire, in this case, is important not only to the species directly affected but also to many other organisms whose survival depends on those key plants. Diversity is low in harsh environments because of the intolerance of all but opportunistic and highly resistant species to such conditions. The interplay between disturbance and these biological processes seems to account for a major portion of the organization and spatial patterning of natural communities. Disturbance variability and are heavily linked, and as a result require adaptations that help increase plant fitness necessary for survival.

According to Whittaker and Levin (1977) all current discussion (persistence, resilience, stability) of succession considers only secondary succession, which by definition follows disturbance, now widely, and unhelpfully, known as perturbation. Much of the persistent controversy surrounding succession stems from the very different starting points or pioneer states following varied kinds and degrees of disturbance, from which the seral sequence begins. Short questions: Ecological Resilience: In ecology, resilience is the capacity of an ecosystem to respond to a perturbation or disturbance by resisting damage and recovering quickly. Such perturbations and disturbances can include stochastic events such as fires, flooding, windstorms, insect population explosions, and human activities such as deforestation, fracking of the ground for oil extraction, pesticide sprayed in soil, and the introduction of exotic plant or animal species. Disturbances of sufficient magnitude or duration can profoundly affect an ecosystem and may force an ecosystem to reach a threshold beyond which a different regime of processes and structures predominates. Human activities that adversely affect ecosystem resilience such as reduction of biodiversity, exploitation of natural resources, pollution, land use, and anthropogenic climate change are increasingly causing regime shifts in ecosystems, often to less desirable and degraded conditions. Interdisciplinary discourse on resilience now includes consideration of the interactions of humans and ecosystems via socio- ecological systems, and the need for shift from the maximum sustainable yield paradigm to environmental resource management which aims to build ecological resilience through "resilience analysis, adaptive resource management, and adaptive governance". Ecological threshold: Ecological threshold is the point at which a relatively small change or disturbance in external conditions causes a rapid change in an ecosystem. When an ecological threshold

has been passed, the ecosystem may no longer be able to return to its state by means of its inherent resilience. Crossing an ecological threshold often leads to rapid change of ecosystem health. Ecological threshold represent a non-linearity of the responses in ecological or biological systems to pressures caused by human activities or natural processes. Critical load, tipping point and are examples of other closely related terms. Cyclic succession: Cyclic succession is a pattern of vegetation change in which in a small number of species tend to replace each other over time in the absence of large-scale disturbance. Observations of cyclic replacement have provided evidence against traditional Clementsian views of an end-state climax community with stable species compositions. Cyclic succession is one of several kinds of ecological succession, a concept in community ecology. When used narrowly, 'cyclic succession' refers to processes not initiated by wholesale exogenous disturbances or long-term physical changes in the environment. However, broader cyclic processes can also be observed in cases of secondary succession in which regular disturbances such as insect outbreaks can 'reset' an entire community to a previous stage.

Graphic Model of Cyclic Succession These examples differ from the classic cases of cyclic succession discussed below in that entire species groups are exchanged, as opposed to one species for another. On geologic time scales, climate cycles can result in cyclic vegetation changes by directly altering the physical environment.

Community equilibrium and species diversity: In some environments, succession reaches a climax, producing a stable community dominated by a small number of prominent species. This state of equilibrium, called the climax community, is thought to result when the web of biotic interactions becomes so intricate that no other species can be admitted. In other environments, continual small-scale disturbances produce communities that are a diverse mix of species, and any species may become dominant. This nonequilibrial dynamic highlights the effects that unpredictable disturbances can have in the development of community structure and composition. Some species-rich tropical forests contain hundreds of tree species within a square kilometre. When a tree dies and falls to the ground, the resultant space is up for grabs. Similarly, some coral reefs harbour hundreds of fish species, and whichever species colonizes a new disturbance patch will be the victor. With each small disturbance, the bid for supremacy begins anew. Diverse communities are healthy communities. Long-term ecological studies have shown that species- rich communities are able to recover faster from disturbances than species-poor communities.

Intermediate Disturbance Hypothesis (IDH): The Intermediate Disturbance Hypothesis (IDH) states that local species diversity is maximized when ecological disturbance is neither too rare nor too frequent. At high levels of disturbance, due to frequent forest fires or human impacts like deforestation, all species are at risk of going extinct. According to IDH theory, at intermediate levels of disturbance, diversity is thus maximized because species that thrive at both early and late successional stages can coexist. IDH is a nonequilibrium model used to describe the relationship between disturbance and species diversity. IDH is based on the following premises: First, ecological disturbances have major effects on species richness within the area of disturbance. Second, interspecific competition results from

one species driving a competitor to extinction and becoming dominant in the ecosystem. Third, moderate ecological scale disturbances prevent interspecific competition.

Graph shows principles of intermediate disturbance hypothesis: I. at low levels of ecological disturbance species richness decreases as competitive exclusion increases, II. at intermediate levels of disturbance, diversity is maximized because species that thrive at both early and late successional stages can coexist, III. at high levels of disturbance species richness is decreased due an increase in species movement.

CHAOS: Classically, chaos is defined as a lack of order; however, in a scientific context it refers to the lack of predictability of a process or sample. Chaos differs from randomness in that chaotic systems are purely deterministic; that is, they are entirely determined by a set of mathematical formulas and initial conditions, with no random elements involved. Since ancient times, it is often argued that undisturbed ecosystems will approach some form of stable equilibrium, at which the populations of the species are maintained at relatively constant numbers. However, ecological studies have criticized this idea of “the ” by pointing out that species abundances in natural ecosystems may remain in a perpetual state of change. For instance, intransitive competition can lead to a cyclic succession, supporting continued changes in community composition as the dominance is passed on from one species to another in an eternal loop. Recent theory predicts that seasonal forcing of a cyclic succession can produce quasiperiodic and chaotic species fluctuations. Chaos has attracted ecologists’ attention, because it limits the long-term predictability of species abundances and because these nonequilibrium dynamics can potentially sustain a high biodiversity. Chaos is predicted by various mathematical models and has been found in laboratory experiments with insect populations, microbial food webs, and plankton communities. However, field evidence of chaos in natural ecosystems is rare and has never been documented in relation to cyclic succession. Chaos is commonly described as bounded aperiodic dynamics of a deterministic system that exhibits sensitive dependence on initial conditions. Sensitivity to initial conditions implies that small initial differences will grow exponentially in time, such that long term prediction becomes impossible. In practice, however, a clear distinction between deterministic and stochastic fluctuations is often impossible, because the intrinsic dynamics of natural systems are influenced by exogenous stochastic variation. For instance, species fluctuations are not only caused by competition and predation but also affected by “environmental noise” generated by stochastic variation in weather conditions. During recent decades, considerable advances have been made in the analysis of chaos in the presence of noise. In particular, sensitive dependence on initial conditions can be estimated for noisy systems using Lyapunov exponents that quantify the extent to which environmental perturbations are amplified (or damped) by the intrinsic dynamics of the system. The intuitive and popular idea of a balance of nature has been criticized, because species interactions may generate nonequilibrium dynamics, such as oscillations and chaos. Scientist provide a field demonstration of nonequilibrium coexistence of competing species through a cyclic succession at the edge of chaos.

(γ=immigration; r=growth rate)

Experiments by several ecologist results indicate that the community dynamics were at the edge of chaos, shifting back and forth between chaotic and stabilizing dynamics during the cyclic succession. Considering the enormous of natural ecosystems, and the many interacting processes, it is surprising that chaos is not frequently observed in nature, but it can be explained by an operation at ‘the edge’ of

chaos to ensure a high utilization of the resources – to move as far away from thermodynamic equilibrium as possible at the prevailing conditions. The simplest and most intuitive definition of chaos is extreme sensitivity to initial conditions. If a system has chaotic dynamics, then the difference: between the trajectories of two populations that have slightly different initial conditions grows until this is essentially as large as the variation in either trajectory . The difference between trajectories grows exponentially (as in simple exponential growth) through time. In other words, if there is an error in the determination of the initial conditions, the error grows until the error is as large as the signal. Chaos theory is concerned with unpredictable courses of events. The irregular and unpredictable time evolution of many nonlinear and complex linear systems has been named chaos. Chaos is best illustrated by Lorentz’ famous butterfly effect.

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